A variety of human diseases and conditions manifested by cardiac abnormalities or cardiac dysfunction can lead to heart failure. Heart failure is a physiological condition in which the heart fails to pump enough blood to meet the circulatory requirements of the body. The study of such diseases and conditions in genetically diverse humans is difficult and unpredictable. Therefore, there is a need for a model system that facilitates the study of the mechanisms and causes of cardiac diseases and conditions as well as the identification of potential therapeutic targets.
The development of transgenic animal technology has provided significant advances for obtaining more complete information about complex systems in vivo. By manipulating the expression of a gene or genes in vivo, it is possible to gain insight into the roles of such genes in a particular system or to study aspects of the system in a genetically controlled environment.
While successful transgene experiments have been performed in a number of large and small animal species, the mouse has been the animal of choice for cardiovascular studies. See, for example, U.S. Pat. No. 6,353,151, herein incorporated by reference. Cardiac preferred transgenesis has been used to establish structure-function relationships between the presence or absence of a particular protein (or its mutated form) and normal or abnormal cardiac function at the molecular, cellular, and physiological levels. However, even with cardiac-preferred promoters, transgenesis can be a blunt instrument, particularly when studying powerful biological signaling proteins that in low abundance can have pleiotropic effects on cardiovascular structure, metabolism, and function. For example, the murine a-myosin heavy chain promoter initiates transcription in the early heart tube, as well as in the developing atria; thus transgene expression from the murine α-myosin heavy chain promoter throughout development has the potential of confounding the post-term phenotype.
Therefore, multiple laboratories have directed efforts at the development of conditional or inducible transgenic systems. One of the most widely used conditional systems is the binary, tetracycline-based system, which has been widely used in both cells and animals to reversibly induce expression by the addition or removal of tetracycline or its analogues. (See Bujard (1999). J. Gene Med. 1:372–374; Furth, et al. (1994). Proc. Natl. Acad. Sci. USA 91:9302–9306; and Mansuy & Bujard (2000). Curr. Opin. Neurobiol. 10:593–596, herein incorporated by reference in their entirety.)
Despite the potential advantages of the tetracycline target gene induction/inactivation system described above, few successes have been reported in the heart. The paucity of data from the cardiovascular system implies that the above described binary system is not robust in cardiac tissue and precludes routine success. Additionally, these systems require development of large numbers of transgenic lines to obtain a working pair of transgenics suitable for regulated, cardiac-preferred transgenic experiments. Furthermore, certain activator transgene constructs induce cardiopathic phenotypes in host animals, even when the animal does not contain a target transgene or responder construct. The presentation of a cardiopathic phenotype in the absence of target transgenes renders these animals less than ideal for use as transgenic models of cardiopathies and heart diseases.
Thus, development of a regulatable, transgenic model system is desirable for use in studying heart disease and conditions. It is of importance to develop a regulated, cardiac-preferred, transgenic expression system that allows controlled expression of a target transgene during any stage of development. It is of particular importance to develop a model transgenic system for studying cardiopathies.